1. Field of the Invention
The present invention relates to a cleaning method and apparatus and, more particularly, to a cleaning method and apparatus suitable for cleaning the surface of a substrate such as a semiconductor substrate and a liquid crystal substrate.
2. Description of the Prior Art
In the manufacture of a semiconductor device, to clean the semiconductor substrate having a surface on which semiconductor elements are formed at a high density is an indispensable important step. As the semiconductor devices are integrated and micropatterned, to effectively remove even fine-particle contamination is necessary in order to improve the yield of the manufacture of the semiconductor devices. In particular, after a film deposition step or a dry etching step where particle contamination tends to occur, cleaning with an ammonia-hydrogen peroxide solution mixture is conventionally performed.
A wet cleaning method using such a chemical solution causes excessive etching and degrades the reliability of the device. In addition, since a large amount of chemical solution must be used, the load to the environment increases. To replace this wet cleaning technique, Ar aerosol cleaning is under development.
According to Ar aerosol cleaning, first, Ar gas is precooled by using liquid nitrogen or a refrigerating machine. The precooled Ar gas is sprayed into a low-pressure space through spray nozzle holes to cause adiabatic expansion, so that a fluid containing solidified fine Ar particles (this liquid will be referred to as Ar aerosol hereinafter) is generated. This Ar aerosol is blown toward the wafer to bombard the solidified fine particles described above against the wafer to remove particle contamination on the wafer and side-wall deposition films (this cleaning method will be referred to as Ar aerosol cleaning hereinafter).
FIG. 1 shows a schematic diagram of a conventional cleaning apparatus. The wafer stage is moved back and forth with respect to spray nozzle holes 4a so as to blow Ar aerosol 5 sprayed from the spray nozzle holes 4a toward the entire surface of a wafer 8. This method is disclosed in the specification of Japanese Unexamined Patent Publication No. 6-283488. Referring to FIG. 1, a rod-like nozzle unit 4 is arranged to be substantially perpendicular to the moving direction of the wafer 8 and to be parallel to the wafer 8. The Ar aerosol 5 sprayed from the spray nozzle holes 4a blows off contaminant particles 7 attaching to the wafer 8. The free contaminant particles 7 are removed in a direction substantially parallel to the substrate.
According to the conventional Ar aerosol cleaning apparatus, since fine Ar particles (Ar aerosol) are blown toward only the upper surface of the wafer, the lower surface of the wafer cannot be processed, leading to a low processing efficiency. Since the Ar aerosol and the free contaminant particles are removed in the horizontal direction, unless the exhaust system is well devised, the contaminant particles may fall on the substrate to attach to it again.